There is a known device which supplies liquid, such as ink, in the form of a succession of drops to a printing apparatus, for example a dot-matrix printer. The known device has an outer and inner chamber interconnected through an inner capillary opening. The inner chamber has a wall which is formed by a diaphragm that is moved by means of the oscillations of a piezoelectric crystal. The diaphragm is arranged to curve inwardly toward the inner chamber and cause a pressure increase therein. Fluid, for example ink, from the inner chamber will then be ejected at a substantial velocity through the inner capillary and then into the outer chamber. The latter contains a thin liquid layer communicating with an ink reservoir. A thin wall represents the outer wall of the outer chamber against the medium on which the print is to be applied. The thin wall is provided with an outlet capillary located opposite to the inner capillary. In this arrangement, a liquid plug is ejected from the inner capillary which strikes the outlet capillary expelling the liquid therein in the form of a liquid drop. This release of the printing ink liquid in the form of drops continues until the voltage on the piezoelectric crystal is removed and the diaphragm returns to a normal position. A negative pressure is then created in the inner chamber which is transferred to the outer chamber by means of the inner capillary. The pressure is equalized by means of liquid being drawn in from a reservoir communicating with the outer liquid layer or by the liquid column in the outlet capillary being drawn back against the action of the capillary force. Since the resistance of the liquid layer in the outer chamber is considerably smaller than the resistance emanating from the capillary force, the liquid required to equalize the pressure will flow from the aforesaid liquid layer. Thus, the known device operates like a pump by drawing liquid in from the outer chamber and forcing the liquid out through the outlet capillary.
It should be pointed out that the prior art device has a number of disadvantages. For example, the closed inner chamber can be filled with liquid only by drawing a large vacuum on the entire system which causes a liquid reservoir of atmospheric pressure to be connected to said inner chamber. Inasmuch as it is not possible to achieve an absolute vacuum, a certain quantity of air in the form of an air cushion will remain in the inner chamber. When the diaphragm is acted upon, this air cushion will be compressed along with the liquid resulting in the reduced efficiency of the device. This occurs because the reduction of volume caused by the movement of the diaphragm is so small that even a small quantity of air causes a reduction of the volume of the air cushion instead of causing such a pressure increase as would have occurred in an incompressible medium. Another disadvantage of the prior art construction is that both the inner and outer chambers of the device are bounded by thin walls which are difficult to stabilize to prevent vibration during pressure changes in the chambers. The wall thickness is determined by the length of the capillaries which is in the order of 0.1 mm. Because of the small length of the capillaries there is a great risk of air being drawn into the system. Furthermore, because the length and width of each capillary as well as the thickness of the outer liquid layer are approximately 0.1 mm, the fabrication of the known device is complicated and expensive. Still another disadvantage of the known device is that the holes in the device must be centered absolutely opposite to each other along a straight line. As a result, the manufacturing tolerance requirements are extremely great when boring the holes and the mounting of the front wall of the device.
The present invention relates to an ink printer of the jet type in which liquid from one or more pump chambers is conducted to one or more outlet channels.
It is an object of the present invention to provide an ink printer supply arrangement which is simple and inexpensive to manufacture and assemble.
Another object of the present invention is to provide an ink supply and pumping arrangement having two opposite plates in which one plate has pumping means disposed in holes or recesses and the second plate has grooves at the surface thereof which faces the other plate. The pumping chambers are formed by the spaces between the pumping means and the second plate. Furthermore, the spaces communicate with the outlet channels.